Oliver Nowak and Marcel Lahaye Media Computing Group RWTH Aachen University

Winter term 2020/21 https://hci.rwth-aachen.de/dis

Lab 1: Fitts’ Law, CMN Model, Assignment 1: Fitts’ Law

Designing Interactive Systems 1

Prof. Dr. Jan Borchers: Designing Interactive Systems I • WS 2020/212

Fitts’ Law

Prof. Dr. Jan Borchers: Designing Interactive Systems I • WS 2019/203

In-Class Exercise 2• How much faster does calling become by moving

the “call” button from 70 mm distance to 30 mm distance, measured from the middle of the keypad? The size of the call button is 10 x 10 mm

• Shannon’s formulation:

• Use a = 0 ms, b = IM =100 ms/bit 1 2 3

654

7 8 9

#0*

70 mm

30 mm

Prof. Dr. Jan Borchers: Designing Interactive Systems I • WS 2019/204

Solution

⇒ Moving the call button speeds up each call by an average of about 100 ms.

Tpos1 = IM · log2

(

D1

W+ 1

)

Tpos2 = IM · log2

(

D2

W+ 1

)

Tpos1 − Tpos2 = IM ·

(

log2

(

D1

W+ 1

)

− log2

(

D2

W+ 1

))

= 100ms

bit·

(

log2

(

70

10+ 1

)

− log2

(

30

10+ 1

))

bit

= 100 ms · (log28 − log24)

= 100 ms · (3 − 2)

= 100 ms

Prof. Dr. Jan Borchers: Designing Interactive Systems I • WS 2019/205

In-Class Exercise 3• Task: Calculate the average time (in ms) needed to reach the button.

• You don’t need a calculator

�ʚ��FP

�ʚ��FP

45º

���FP

Shannon’s Formula : Tpos = a + b · log2

(

D

W+ 1

)

a = 0 ms

b = IM = 100ms

bit

Solution

Prof. Dr. Jan Borchers: Designing Interactive Systems I • WS 2019/206

Shannon’s Formula : Tpos = a + b · log2

(

D

W+ 1

)

a = 0 ms

b = IM = 100ms

bit

Tpos = 0 ms + 100ms

bit· log2

(

36

12+ 1

)

bit

= 200 ms

�ʚ��FP

�ʚ��FP

45º

���FP

Side of the square, r = 6√

2 cm

Target width, W =√

r 2 + r 2 cm

= r

√

2 cm

= 6√

2 ·

√

2 cm

= 12 cm

Distance, D = 36 cm

Prof. Dr. Jan Borchers: Designing Interactive Systems I • WS 2019/207

In-Class Exercise #4: Prime Locations for Targets

7

Prof. Dr. Jan Borchers: Designing Interactive Systems I • WS 2019/208

In-Class Exercise #5: Pop-up Menus• Which of the following pop-up menus lead to a faster selection time?

A

B

C

D

E

F

Vertical

A B C D E F

Horizontal

A

B C

D

EF

Radial

8

Prof. Dr. Jan Borchers: Designing Interactive Systems I • WS 2019/209

CMN Model

In-Class Exercise 1• A letter or a number is displayed randomly

• User has to press A (left) or press L (right) accordingly

• Assumption: user’s fingers are already on these keys

• Calculate the average time the user needs to press the correct button

Prof. Dr. Jan Borchers: Designing Interactive Systems I • WS 2019/2010

Solution • Perceptive: 100 ms

• Cognitive (semantic recognition): 70 ms

• Cognitive (categorization): 70 ms

• Cognitive (left or right?): 70 ms

• Cognitive (do something!): 70 ms

• Motor: 70 ms

• Adds up to approximately 450 ms

Prof. Dr. Jan Borchers: Designing Interactive Systems I • WS 2019/2011

Assignment I: Fitts’ Law• Objective: Learn how to apply Fitts’ law in interface design

• Assignment is available online on RWTHmoodle now!

• Deadline: Next Monday, Nov. 09, 02:30 p.m.

• Use RWTHmoodle to submit (1 submission per group)

• Submissions after deadline will be graded 5.0

• Name your file A01-GXX.pdf, where XX indicates your group number. E.g., if you are in group 5, name your PDF document as A01-G05.pdf. We will reduce points for incorrectly named files

• A few of you will be asked to present your solution during the next lab

• You should have the possibility to form groups of three in Moodle by now (Deadline Tomorrow 08:00 a.m.)

Prof. Dr. Jan Borchers: Designing Interactive Systems I • WS 2019/2012